Protective film temporarily lamination to electromagnetic wave shielding sheet, method for producing the same, and electromagnetic wave shielding sheet

ABSTRACT

The present invention is to provide an electromagnetic wave shielding sheet with a protective film that is temporarily laminated on a copper mesh layer for shielding electromagnetic waves, the electromagnetic wave shielding sheet is not discolored even after long-term use, especially at high temperature and high humidity, while the protective film exhibits appropriate adhesion properties. To achieve the object, there is provided an electromagnetic wave shielding sheet comprising a transparent substrate, at least a copper mesh layer provided on one surface of the transparent substrate and a protective film temporarily laminated to the copper-mesh-layer-side surface, the protective film comprises a support and an adhesive layer containing a polymer having repeating units derived from an acrylic ester and/or a methacrylic ester on the support, and the amount of free organic acids in the adhesive layer is an amount which makes 10 or less the color difference ΔE L*a*b*  of the copper-mesh-layer-side surface of the electromagnetic wave shielding sheet before and after the adhesive layer surface is laminated on the copper-mesh-layer-side surface and they are left for 200 hours in an atmosphere of a temperature of 60° C. and a relative humidity of 95%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic wave shielding sheetto shield electromagnetic waves produced from displays such ascathode-ray tubes (CRT) or plasma display panels (PDP.) In particular,the present invention relates to a protective film that causes nodiscoloration of an electromagnetic wave shielding sheet even afterlong-term storage at high temperature and high humidity, a method forproducing the protective film, and an electromagnetic wave shieldingsheet with the protective film.

2. Description of the Related Art

With the sophistication of function and the increasing use of electricaland electronic devices in recent years, electromagnetic interference(ERI) has increased and displays such as cathode-ray tubes and plasmadisplay panels produce electromagnetic waves. To shield theelectromagnetic waves, electromagnetic wave shielding sheets to bedisposed on the front face of a display is known. Such electromagneticwave shielding sheets are demanded to have optical transparency as wellas electromagnetic wave shielding capability. Accordingly,electromagnetic wave shielding sheets provided with optical transparencyby using a transparent substrate such as a resin film or a glass plateas a substrate and forming thereon a conductive mesh layer of metal suchas copper are known.

Sometimes optical filters such as an antireflection filter and anear-infrared filter are mounted on the front face of a display so thatin many cases an electromagnetic wave shielding sheet is laminated tothe optical filters through an adhesive layer and disposed on the frontsurface of a display as a composite filter. For example, Japanese PatentApplication Laid-Open (JP-A) No. 11-126024 discloses a front surfaceplate of a display panel in which an antireflection film is attached toa filter film for shielding electromagnetic waves through a tackyadhesive layer.

Sometimes a protective film is temporarily laminated to theelectromagnetic wave shielding sheet to protect the mesh layer until theelectromagnetic wave shielding sheet is disposed on the front face of adisplay or laminated to other optical filters, etc. JP-A No. 2003-188576discloses an electromagnetic wave shield sheet comprising a protectivefilm to protect a transparent base film or an electromagnetic waveshielding layer in handling or production of the products.

SUMMARY OF THE INVENTION

As aforementioned, during the time between forming a conductive meshlayer on a transparent substrate and treating the mesh layer surfacewith various post-processes such as providing an adhesive layer thatwill function as a planarizing layer of the mesh layer and laminatingthe adhesive layer to another optical film or a display, preferably aprotect film is temporarily laminated to the mesh layer surface to keepthe concave of the conductive mesh layer free of dust or to make meshlines of the conductive mesh layer having an extremely narrow width ofabout 10 μm free from contamination or breaking. In order to laminate aprotective film directly to such a mesh layer surface, the protectivefilm is required to have appropriate adhesion properties that allow theprotective film to directly adhere to and easily peel off the conductivemesh layer, and use of a film having an adhesive layer has been studied.However, at the time of peeling off a protective film, some adhesivescause problems such that a blackened layer that is further laminated ona copper mesh layer is partially peeled off together with the protectivefilm and adhesive residue is left behind. In the case where a filmhaving an adhesive layer is temporarily laminated to a conductive meshlayer such as a copper mesh layer, some adhesives cause a problem ofblue-green discoloration of the copper mesh layer when theelectromagnetic wave shielding sheet is stored for a longtime,especially at high temperature and high humidity. Such discoloration ofa copper mesh layer causes blue discoloration of the electromagneticwave shielding sheet and the color reproducibility of a display isadversely affected. This problem also occurs when a blackened layercomprising a thin film of cooper-cobalt alloy particles, nickel sulfideparticles or the like is formed on a copper mesh and an adhesive layeris laminated thereon.

The present invention has been achieved in light of the above-statedproblems. The object of the present invention is firstly to provide aprotective film for temporary lamination to an electromagnetic waveshielding sheet, which film leaves no adhesive residue behind whenpeeled off and causes no partial peeling of a blackened layer and thelike if the blackened layer and the like are further laminated on thecopper mesh layer, while the film having appropriate adhesion propertiesthat involves easy adhesion and easy peelability in a balanced mannerwith respect to a copper mesh layer of the electromagnetic waveshielding sheet. Especially, the present invention is to provide aprotective film for temporary lamination to an electromagnetic waveshielding sheet that causes no discoloration of the electromagnetic waveshielding sheet even after long-term use, especially at high temperatureand high humidity.

The object of the present invention is secondly to provide anelectromagnetic wave shielding sheet with a protective film that istemporarily laminated on a copper mesh layer for shieldingelectromagnetic waves, the protective film leaves no adhesive residuebehind when peeled off and causes no partial peeling of a blackenedlayer and the like if the blackened layer and the like are furtherlaminated on the copper mesh layer, while the copper mesh layer and theprotective film exhibit easy adhesion and easy peelability. Especially,the present invention is to provide an electromagnetic wave shieldingsheet that does not discolor even after long-term use, especially athigh temperature and high humidity.

In order to achieve the first object, the present invention provides aprotective film for temporary lamination to an electromagnetic waveshielding sheet in which at least a copper mesh layer is provided on onesurface of a transparent substrate, wherein the protective film is fortemporary lamination to a copper-mesh-layer-side surface of theelectromagnetic wave shielding sheet; the protective film comprises asupport and an adhesive layer containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester on thesupport; and an amount of free organic acids in the adhesive layer is anamount that makes 10 or less a color difference ΔE_(L*a*b*) of thecopper-mesh-layer-side surface of the electromagnetic wave shieldingsheet before and after the adhesive layer surface is laminated on thecopper-mesh-layer-side surface and they are left for 200 hours in anatmosphere of a temperature of 60° C. and a relative humidity of 95%.

In order to achieve the first object, the present invention alsoprovides a protective film for temporary lamination to anelectromagnetic wave shielding sheet, wherein the protective filmcomprises a support and an adhesive layer containing a polymer havingrepeating units derived from an acrylic ester and/or a methacrylic esteron the support; and 20 ng/cm² or less is a total amount of acetic acidand formic acid extracted upon testing the protective film by a testmethod in which the adhesive layer surface of the protective film isextracted at 23° C. for 15 minutes with ultrapure water and theresulting extract is measured for an amount of extracted acetic acid andan amount of extracted formic acid by ion chromatography.

In order to achieve the first object, the present invention furtherprovides a protective film for temporary lamination to anelectromagnetic wave shielding sheet, wherein the protective filmcomprises a support and an adhesive layer containing a polymer havingrepeating units derived from urethane acrylate and/or urethanemethacrylate on the support.

Further, the present invention provides a method for producing aprotective film for temporary lamination to a copper-mesh-layer-sidesurface of an electromagnetic wave shielding sheet in which at least thecopper mesh layer is provided on one surface of a transparent substrate,the method comprising the steps of: selecting an adhesive in which anamount of free organic acids is an amount that makes 10 or less a colordifference ΔE_(L*a*b*) of the copper-mesh-layer-side surface of theelectromagnetic wave shielding sheet before and after the adhesive islaminated on the copper-mesh-layer-side surface and they are left for200 hours in an atmosphere of a temperature of 60° C. and a relativehumidity of 95%, from adhesives containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester, andtherewith forming an adhesive layer on a support.

In order to achieve the second object, the present invention provides anelectromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of thetransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises asupport and an adhesive layer containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester on thecopper mesh layer side of the support, and an amount of free organicacids in the adhesive layer is an amount that makes 10 or less a colordifference ΔE_(L*a*b*) of the copper-mesh-layer-side surface of theelectromagnetic wave shielding sheet before and after the adhesive layersurface is laminated on the copper-mesh-layer-side surface and they areleft for 200 hours in an atmosphere of a temperature of 60° C. and arelative humidity of 95%.

Also, in order to attain the second object, the present inventionprovides an electromagnetic wave shielding sheet comprising: atransparent substrate; at least a copper mesh layer provided on onesurface of the transparent substrate; and a protective film temporarilylaminated to a copper-mesh-layer-side surface, wherein the protectivefilm comprises a support and an adhesive layer containing a polymerhaving repeating units derived from an acrylic ester and/or amethacrylic ester on the copper mesh layer side of the support; theprotective film is temporarily laminated to the copper-mesh-layer-sidesurface through the adhesive layer; and 20 ng/cm² or less is a totalamount of acetic acid and formic acid extracted upon testing theprotective film by a test method in which the adhesive layer surface ofthe protective film is extracted at 23° C. for 15 minutes with ultrapurewater and the resulting extract is measured for an amount of extractedacetic acid and an amount of extracted formic acid by ionchromatography.

In order to attain the second object, the present invention alsoprovides an electromagnetic wave shielding sheet comprising: atransparent substrate; at least a copper mesh layer provided on onesurface of a transparent substrate; and a protective film temporarilylaminated to a copper-mesh-layer-side surface, wherein the protectivefilm comprises a support and an adhesive layer containing a polymerhaving repeating units derived from urethane acrylate and/or urethanemethacrylate on the copper mesh layer side of the support.

According to the present invention, since the protective film comprisesan adhesive layer containing a polymer having repeating units derivedfrom an acrylic ester and/or a methacrylic ester, and the amount of freeorganic acids in the adhesive layer is an amount that makes 10 or less acolor difference ΔE_(L*a*b*) of the copper-mesh-layer-side surface ofthe electromagnetic wave shielding sheet before and after the adhesivelayer surface is laminated on the copper-mesh-layer-side surface andthey are left for 200 hours in an atmosphere of a temperature of 60° C.and a relative humidity of 95%, the following effects can be produced.While the copper mesh layer and the protective film appropriatelyexhibit easy adhesion and easy peelability, the protective film leavesno adhesive residue behind when peeled off and causes no partial peelingof a blackened layer and the like that are further laminated on thecopper mesh layer. In addition, the protective film causes nodiscoloration of the copper mesh layer even after long-term use,especially at high temperature and high humidity.

According to the present invention, since the protective film comprisesan adhesive layer containing a polymer having repeating units derivedfrom an acrylic ester and/or a methacrylic ester, and 20 ng/cm² or lessis the total amount of acetic acid and formic acid extracted upontesting the protective film by the above-specified test method, thefollowing effects can be produced. While the copper mesh layer and theprotective film appropriately exhibit easy adhesion and easypeelability, the protective film leaves no adhesive residue behind whenpeeled off and causes no partial peeling of a blackened layer and thelike that are further laminated on the copper mesh layer. In addition,the protective film causes no discoloration of the copper mesh layereven after long-term use, especially at high temperature and highhumidity.

In the present invention, since the protective film comprises anadhesive layer containing a polymer having repeating units derived fromurethane acrylate and/or urethane methacrylate, the following effectscan be produced. While the copper mesh layer and the protective filmexhibit easy adhesion and easy peelability, the protective film leavesno adhesive residue behind when peeled off and causes no partial peelingof a blackened layer and the like that are further laminated on thecopper mesh layer.

In the electromagnetic wave shielding sheet of the present invention,delamination resistance of the adhesive layer of the protective film ispreferably from 0.05 to 1.3 N/25 mm with respect to thecopper-mesh-layer-side surface from the viewpoint of appropriateadhesion that allows the protective film to directly adhere to andeasily peel off the copper mesh layer.

In the electromagnetic wave shielding sheet of the present invention,surface roughness of the copper-mesh-layer-side surface to which theprotective film is temporarily laminated is preferably a ten-pointaverage roughness “Rz JIS” (JIS B0601 (1994)) of the profile from 0.5 to5.0 μm when a roughness profile is used as a profile of the surface, anda center line average roughness “Ra” (JIS B0601 (1994)) of fineirregularities on the surface from 0.1 to 3.0 μm from the viewpoint ofappropriate adhesion and removability when combined with an adhesivespecified in the present invention, that is, the protective film leavesno adhesive residue behind when peeled off and causes no partial peelingof a blackened layer and the like if the blackened layer and the likeare further laminated on the copper mesh layer, while having easyadhesion and easy peelability.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a sectional view illustrating an example of a protective filmfor temporary lamination to an electromagnetic wave shielding sheetaccording to the present invention.

FIG. 2A is a sectional view illustrating an example of theelectromagnetic wave shielding sheet according to the present invention.

FIG. 2B is a sectional view illustrating an example of theelectromagnetic wave shielding sheet according to the present invention.

FIG. 2C is a sectional view illustrating an example of theelectromagnetic wave shielding sheet according to the present invention.

FIG. 3 is a perspective view of an example (FIG. 2C) of theelectromagnetic wave shielding sheet according to the present invention.

FIG. 4A is a sectional view taken along the line A-A of FIG. 3.

FIG. 4B is a sectional view taken along the line B-B of FIG. 3.

FIG. 5 is a diagram illustrating a laminating machine to temporarilylaminate the electromagnetic wave shielding sheet and the protectivefilm of the present invention.

FIGS. 6A to 6D are diagrams illustrating an example of producing theelectromagnetic wave shielding sheet according to the present invention.

The numerical symbol in each figure refers to the following: 1. support;2. adhesive layer; 11. transparent substrate; 12. conductor layer; 13.conductive treating layer; 14. copper mesh layer; 15. copper platedlayer; 17. blackened layer; 18. metal layer; 20, 30, 40. laminate; 21.first paper feed member; 22. second paper feed member; 23. first releasefilm wind-up roller; 24. second release film wind-up roller; 25. firstlaminating unit; 26. second laminating unit; 27. wind-up roller; 100.electromagnetic wave shielding sheet; 101. mesh area; 103. opening; and104. line

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a protective film for temporarylamination to an electromagnetic wave shielding sheet and anelectromagnetic wave shielding sheet. Hereinafter, a protective film fortemporary lamination to an electromagnetic wave shielding sheet and anelectromagnetic wave shielding sheet will be described in this order.

A. Protective Film for Temporary Lamination to Electromagnetic WaveShielding Sheet

Now, the protective film for temporary lamination to the electromagneticwave shielding sheet of the present invention is described.

The first protective film for temporary lamination to an electromagneticwave shielding sheet of the present invention is a protective film fortemporary lamination to an electromagnetic wave shielding sheet in whichat least a copper mesh layer is provided on one surface of a transparentsubstrate, wherein the protective film is for temporary lamination to acopper-mesh-layer-side surface of the electromagnetic wave shieldingsheet; the protective film comprises a support and an adhesive layercontaining a polymer having repeating units derived from an acrylicester and/or a methacrylic ester on the support; and an amount of freeorganic acids in the adhesive layer is an amount that makes 10 or less acolor difference ΔE_(L*a*b*) of the copper-mesh-layer-side surface ofthe electromagnetic wave shielding sheet before and after the adhesivelayer surface is laminated on the copper-mesh-layer-side surface andthey are left for 200 hours in an atmosphere of a temperature of 60° C.and a relative humidity of 95%.

The second protective film for temporary lamination to anelectromagnetic wave shielding sheet of the present invention is aprotective film for temporary lamination to an electromagnetic waveshielding sheet, wherein the protective film comprises a support and anadhesive layer containing a polymer having repeating units derived froman acrylic ester and/or a methacrylic ester on the support, and 20ng/cm² or less is a total amount of acetic acid and formic acidextracted upon testing the protective film by a test method in which theadhesive layer surface of the protective film is extracted at 23° C. for15 minutes with ultrapure water and the resulting extract is measuredfor an amount of extracted acetic acid and an amount of extracted formicacid by ion chromatography.

The third protective film for temporary lamination to an electromagneticwave shielding sheet is a protective film for temporary lamination to anelectromagnetic wave shielding sheet, wherein the protective filmcomprises a support and an adhesive layer containing a polymer havingrepeating units derived from urethane acrylate and/or urethanemethacrylate on the support.

Temporarily laminating a temporary protective film to the copper meshlayer surface of the electromagnetic wave shielding sheet has advantagessuch that during the time until the next process, the concave portion ofthe conductive mesh layer can be kept free of dust and the mesh linescan be free from breaking or contamination upon handling or storage. Inthe case of temporarily laminating a film having an adhesive layer to acopper mesh layer, however, some adhesives cause problems such thatadhesive residue is left behind when a temporarily laminated protectivefilm is peeled off and a blackened layer and the like that are furtherlaminated on the copper mesh layer are partially peeled off togetherwith the protective film. An other problem is that the copper mesh layerdiscolors after the electromagnetic wave shielding sheet is stored for along time, especially at high temperature and high humidity.

In this regard, since the protective film of the present invention usesan adhesive layer containing a polymer having repeating units derivedfrom an acrylic ester and/or a methacrylic ester, especially a polymerhaving repeating units derived from urethane acrylate and/or urethanemethacrylate for the adhesive to form an adhesive layer, the protectivefilm leaves no adhesive residue behind when peeled off and causes nopartial peeling of a blackened layer and the like that are furtherlaminated on the copper mesh layer. In addition, the protective film hasgood adhesion and removability.

Since the protective film comprises an adhesive layer containing apolymer having repeating units derived from an acrylic ester and/or amethacrylic ester and the amount of free organic acids in the adhesivelayer is an amount that makes 10 or less the color differenceΔE_(L*a*b*) of the copper-mesh-layer-side surface before and after theabove-specified test in a high temperature and high humidityenvironment, the protective film leaves no adhesive residue behind whenpeeled off and causes no partial peeling of a blackened layer and thelike that are further laminated on the copper mesh layer, while thecopper mesh layer and the protective film exhibit appropriate adhesionproperties. In addition, the protective film allows no discoloration ofthe electromagnetic wave shielding sheet even after long-term use,especially at high temperature and high humidity. It is noted the term“free organic acids” refers to organic compounds having a carboxyl groupthat is present in uncombined form and examples of the free organicacids include acetic acid and formic acid.

Alternatively, since the protective film comprises an adhesive layercontaining a polymer having repeating units derived from an acrylicester and/or a methacrylic ester and 20 ng/cm² or less is the totalamount of acetic acid and formic acid extracted from the adhesive layersurface upon testing the protective film by the above-specified testmethod, the protective film leaves no adhesive residue behind whenpeeled off and causes no partial peeling of a blackened layer and thelike that are further laminated on the copper mesh layer, while thecopper mesh layer and the protective film exhibit appropriate adhesionproperties. In addition, the protective film allows no discoloration ofthe electromagnetic wave shielding sheet even after long-term use,especially at high temperature and high humidity.

The reasons that the copper mesh layer of the electromagnetic waveshielding sheet and the protective film exhibit appropriate adhesionproperties and the protective film used in the present invention causesno discoloration of the electromagnetic wave shielding sheet even afterlong-term use, especially at high temperature and high humidity, areconsidered as follows.

An adhesive layer containing a polymer having repeating units derivedfrom an acrylic ester and/or a methacrylic ester, especially an adhesivelayer containing a polymer having repeating units derived from urethaneacrylate and/or urethane methacrylate, is found suitable and selected asone having good adhesion and removability, i.e. one that hardly leavesadhesive residue behind when peeling off a protective film and causes nopartial peeling of a blackened layer and the like that are furtherlaminated on the copper mesh layer, while having appropriate adhesionproperties that allows the adhesive layer to directly adhere to andeasily peel off the conductive mesh layer. On the other hand,discoloration of the copper mesh layer after long-term storage at hightemperature and high humidity is attributed to that the presence ofprotons dissociated from acids and so on and water contained in theadhesive layer renders the copper surface sensitive to oxidation so thatcompounds containing copper ions such as copper complex is produced byoxidation, thereby discoloring the copper surface to blue or similarcolor.

It seems that in general carboxyl groups or acid components can bepresent in an adhesive layer containing a polymer having repeating unitsderived from an acrylic ester and/or a methacrylic ester.

To the contrary, while the adhesive layer of the protective film of thepresent invention is an adhesive layer containing a polymer havingrepeating units derived from an acrylic ester and/or a methacrylicester, the amount of free organic acids in the adhesive layer is assmall as an amount that makes 10 or less the color differenceΔE_(L*a*b*) of the copper-mesh-layer-side surface before and after theabove-specified test in a high temperature and high humidityenvironment.

Also, while the adhesive layer of the protective film of the presentinvention is an adhesive layer containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester, thetotal amount of acetic acid and formic acid extracted from the adhesivelayer surface in a test conducted by the above-specified test method isas small as 20 ng/cm² or less.

As aforementioned, among the acid components contained in the adhesivelayer, the present invention focuses on free organic acids that arecapable of readily transferring to the adhesive layer surface to be incontact with the electromagnetic wave shielding sheet or specific freeorganic acids that are present on the adhesive layer surface. It ispresumed that reducing the amount of the free organic acids allows todecrease the presence of protons dissociated from the adhesive layersurface to be in contact with the electromagnetic wave shielding sheetso as to control the oxidation-sensitive state of the copper surfaceeven in high temperature and high humidity environment. Consequently, itseems possible to obtain an electromagnetic wave shielding sheet thatdoes not discolor even after long-term use, especially at hightemperature and high humidity, by using the above-described adhesivelayer as an adhesive layer to be in contact with the copper mesh layersurface of the electromagnetic wave shielding sheet.

(Layer Configuration)

FIG. 1 is a sectional view showing a basic embodiment of the protectivefilm for temporary lamination to the electromagnetic wave shieldingsheet according to the present invention.

FIG. 1 shows a configuration of a protective film 10 for temporarylamination to an electromagnetic wave shielding sheet, in which anadhesive layer 2 containing a polymer having repeating units derivedfrom an acrylic ester and/or a methacrylic ester is laminated on asupport 1.

A release layer (not shown in FIG. 1) may be further laminated on thesurface of the support 1, on which the adhesive layer 2 is notlaminated. Also, the release layer may be laminated to the adhesivelayer 2 until the protective film for temporary lamination to anelectromagnetic wave shielding sheet is actually laminated to anelectromagnetic wave shielding sheet.

The embodiments of the protective film for temporary lamination to theelectromagnetic wave shielding sheet of the present invention are notlimited by the above-mentioned examples. Any that has the substantiallysame essential features as the technical ideas described in claims ofthe present invention and exerts the same effects and advantages isincluded in the technical scope of the present invention.

Hereinafter, the protective film of the present invention will bedescribed.

(Support)

The support is a layer having strength to support the adhesive layerhaving low mechanical strength and to protect the mesh surface of theelectromagnetic wave shielding sheet. Consequently, there is noparticular limit to the support and as far as it has strength to supportthe adhesive layer and to protect the mesh surface, and suitableproperties for storage. It may be appropriately selected for usedepending on storage conditions. Concrete examples of the supportinclude a film or sheet of organic material such as resin. Such film orsheet is suitable for use since it is sufficiently thin, lightweight,flexible and strong.

Resins used to form the film or sheet of organic material include, forexample, polyester resin such as polyethylene terephthalate,polybutylene terephthalate, polyethylene naphthalate, copolymer ofterephthalic acid, isophthalic acid and ethylene glycol, copolymer ofterephthalic acid, cyclohexanedimethanol and ethylene glycol; polyamideresin such as nylon 6; polyolefin resin such as polyethylene,polypropylene, polymethylpentene; polyvinyl chloride; and so on.

There is no particular limit to the thickness of the support as far asit meets the storage conditions of the electromagnetic wave shieldingsheet. The thickness is normally from 25 to 70 μm, preferably from 40 to60 μm. The support having a thickness less than the range isinsufficient in mechanical strength and may break. The support having athickness exceeding the range is excess in performance and expensive. Inaddition, it is difficult to wind for storage.

A resin film or sheet is a preferable material for the support. Amongresins, polyolefins such as polyethylene, polypropylene are particularlypreferable since they are excellent in transparency, easy to peel forits balance between elasticity and flexibility, and inexpensive.Especially, polypropylene is preferable since it does not stretch easilyand hardly causes curling or partial detachment of the protective filmafter adhesion. In addition, for these reasons, the selection toleranceof delamination resistance of the adhesive is widened.

(Adhesive Layer)

The adhesive layer provided with the protective film of the presentinvention needs to have the above-mentioned excellent adhesion andremovability. Further, the copper mesh layer surface (especially, a thinand rough or porous blackened layer) to which the protective film willadhere is required not to peel off with the adhesive. As a result ofconsidering various resins, an acrylic polymer, that is, one containinga polymer having repeating units derived from an acrylic ester and/or amethacrylic ester is found excellent. The adhesive layer provided withthe protective film of the present invention may contain a compound suchas an additive (e.g. antioxidant) as needed. Rubber adhesives aregenerally excellent to prevent discoloration of copper. However, in thiscase, since the copper mesh layer surface (especially, the blackenedlayer) is liable to peel off with the adhesive layer at the time ofpeeling off the protective film, they are not suitable for theapplication in which such peeling of the copper mesh layer surface isnot desired.

The term “adhesive” as used herein refers to a kind of bonding agentwhich allows adhesion by simply applying an appropriate, light handpressure with only surface stickiness given by the bonding agent. Ingeneral, the adhesive requires no physical energy or action such asheat, humidity or radiation irradiation (e.g. ultra violet orelectron-beam irradiation) to exhibit its adhesion force. In addition,no chemical reaction such as polymerization reaction is required. Theadhesive can keep a certain adhesion force that is capable of adhesionand removability over time. As the adhesive used in the presentinvention, an acrylic adhesive which mainly comprises repeating unitsderived from an acrylic ester and/or a methacrylic ester and is apolymer obtained by copolymerizing copolymerizable monomers as neededsince the adhesive leaves no adhesive residue behind when peeling offthe protective film and causes no partial peeling of a blackened layerand the like that are further laminated on the copper mesh layer, whilehaving appropriate adhesion properties.

In the case where such an acrylic adhesive is used as an adhesive layer,discoloration of a copper mesh layer may easily occur. However, in theadhesive layer provided with the protective film of the presentinvention, the amount of free organic acids in the adhesive layer is anamount that makes 10 or less the color difference ΔE_(L*a*b*) of thecopper-mesh-layer-side surface, the color difference ΔE_(L*a*b*) isbased on chromaticities a*, b*, and a luminance L* (defined byInternational Commission on Illumination or CIE) of thecopper-mesh-layer-side surface measured before and after the adhesivelayer surface is laminated on the copper-mesh-layer-side surface of theelectromagnetic wave shielding sheet and left for 200 hours in anatmosphere of a temperature of 60° C. and a relative humidity of 95%.Preferably, the amount of free organic acids in the adhesive layer is anamount that makes the color difference ΔE_(L*a*b*) 5 or less. Morepreferably, it is an amount that makes the color difference ΔE_(L*a*b*)1 or less. From the viewpoint of ensuring adhesion to the copper meshlayer, a certain amount of free organic acids may remain in the adhesivelayer as far as the color difference ΔE_(L*a*b*) is 10 or less and 0.1or more. Color difference ΔE_(L*a*b*) is calculated by the followingequation: ΔE_(L*a*b*)={(ΔL*)²+(Δa*)²+(Δb*)²}^(1/2)

It is noted that ΔL*, Δa* and Δb* respectively refer to the differenceof values of L*, a* and b* of the copper-mesh-side surface of theelectromagnetic wave shielding sheet, before and after the sheet is leftto stand in the above-specified environment for the above-specifiedhours. L*, a* and b* are values in L*a*b* color system recommended bythe International Commission on Illumination (CIE) in 1976 and alsodefined in JIS Z8729.

when the copper mesh layer has a color tone of the copper or a colortone of the blackened layer on the copper surface, and the mesh shapeand size of the copper mesh layer is in the ranges of those as will bedescribed, a color difference ΔE_(L*a*b*) of 10 or less is almostinvisible and practically unnoticeable in the case of theelectromagnetic wave shielding sheet comprising the copper mesh disposedon the front face of a normal image display. Especially, a colordifference ΔE_(L*a*b*) of less than the range of 0.6 to 1.0, which rangeis generally regarded as the visually differentiable threshold range, ismore preferable since no discoloration of the copper mesh layer surfacecan be visually differentiated.

The adhesive layer to be provided with the protective film of thepresent invention hardly causes discoloration of the copper mesh layersince an adhesive layer in which the total amount of acetic acid andformic acid obtained by extracting the adhesive layer surface at 23° C.for 15 minutes with ultrapure water measures 20 ng/cm² or less by ionchromatography, is selected as the adhesive layer of the presentinvention. More particularly, a color difference ΔE_(L*a*b*) of 10 orless, more preferably 5 or less, still more preferably 1 or less, isachievable in the case where the adhesive layer surface of theprotective layer of the present invention is laminated to thecopper-mesh-layer-side surface of the electromagnetic wave shieldingsheet; a test in a high temperature and high humidity environment isperformed thereon (i.e., they are left in an environment with atemperature of 60° C. and a relative humidity of 95% for 200 hours); andchromaticities a*, b*, and a luminance L* (defined by InternationalCommission on Illumination or CIE) are measured for thecopper-mesh-layer-side surface before and after the test to obtain acolor difference ΔE_(L*a*b*). The total amount of acetic acid and formicacid extracted from the adhesive layer is more preferably 10 ng/cm² orless, still more preferably 3 ng/cm² or less. From the viewpoint ofensuring adhesion to the copper mesh layer, a certain total amount ofacetic acid and formic acid may remain in the adhesive layer after theextraction. If the total amount of acetic acid and formic acid extractedfrom the adhesive layer in the above-mentioned test is 20 ng/cm² orless, 0.5 ng/cm² or more, or further, 1 ng/cm² or more of acetic acidand formic acid may be contained in the adhesive layer.

Extraction of the adhesive layer surface at 23° C. for 15 minutes withultrapure water has to be performed in a clean booth disposed with achemical filter. The elution amount (ng/cm²) of acetic acid or formicacid per unit area can be obtained by multiplying the concentration ofacetic acid/forming acid in the resulting extract (ng/mL) by the amountof the resulting extract (mL) and then dividing the result by theextraction area (cm².) The total of the amounts obtained by thecalculation is the total elution amount of acetic acid or formic acid.

As the acrylic ester and/or a methacrylic ester used to form a polymerhaving repeating units derived from an acrylic ester and/or amethacrylic ester, monomers such as (meth) acrylic acid alkyl ester,urethane (meth)acrylate obtained by the reaction of hydroxylgroup-containing (meth)acrylic acid ester with isocyanates may besuitably used. Also, (meth)acrylic acid alkoxyalkyl ester or the likemay be used. It should be noted acrylic acid and/or methacrylic acid isreferred to herein as (meth)acrylic acid for brevity. Acrylate and/ormethacrylate is referred to herein as (meth)acrylate.

Examples of the (meth)acrylic acid alkyl ester monomer used hereininclude methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl(meth)acrylate, sec-propyl (meth)acrylate, n-butyl (meth)acrylate,sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, isoamyl(meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate,n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, undecyl (meth)acrylate, and lauryl (meth)acrylate.

As the hydroxyl group-containing (meth) acrylic acid ester used forurethane (meth)acrylate obtained by the reaction of hydroxylgroup-containing (meth)acrylic acid ester with isocyanates,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and so onare suitably used. A compound having in the molecule thereof at leastone isocyanate group may be used as the isocyanates, and divalentisocyanates such as tolylene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-diphenylmethane diisocyanate, hydrogenatedtolylene diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate,lysine diisocyanate methyl ester, 2,2,4-trimethyl hexamethylenediisocyanate and xylylene diisocyanate are preferable. Multimers thereof(e.g. dimers or monomers) or adducts thereof may be used.

Preferable examples of urethane (meth)acrylate include urethane(meth)acrylate obtained by the reaction of 2-hydroxyethyl (meth)acrylatewith tolylene diisocyanate and urethane (meth)acrylate obtained by thereaction of 2-hydroxypropyl (meth)acrylate with tolylene diisocyanate.Especially, urethane methacrylate obtained by the reaction of2-hydroxyethyl methacrylate with tolylene diisocyanate is suitably used.

Examples of the (meth)acrylic acid alkoxyalkyl ester include2-methoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate,2-methoxypropyl (meth)acrylate, 3-methoxypropyl (meth)acrylate,2-methoxybutyl (meth)acrylate, 4-methoxybutyl (meth)acrylate,2-ethoxyethyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate and4-ethoxybutyl (meth)acrylate.

Especially, the polymer having repeating units derived from an acrylicester and/or a methacrylic ester used in the present inventionpreferably has repeating units derived from urethane (meth)acrylate asthe repeating units derived from an acrylic ester and/or a methacrylicester. In this case, it is more achievable that the amount of freeorganic acids in the adhesive layer is an amount that makes 10 or lessthe color difference ΔE_(L*a*b*) of the copper-mesh-layer-side surfacebefore and after the above-specified test in a high temperature and highhumidity environment and the total amount of acetic acid and formic acidextracted by the above-specified test measures 20 ng/cm² or less,

while the adhesive layer has appropriate adhesion properties that allowthe adhesive layer to leave less adhesive residue behind and cause nopartial peeling of a blackened layer and the like that are furtherlaminated on the copper mesh layer of the electromagnetic wave shieldingsheet, when the protective film is peeled off from the electromagneticwave shielding sheet.

Preferable and concrete examples of the polymer having repeating unitsderived from an acrylic ester and/or a methacrylic ester used in thepresent invention include but are not limited to: (1) a copolymer havingrepeating units derived from urethane (meth)acrylate obtained by thereaction of 2-hydroxyethyl (meth)acrylate with tolylene diisocyanate andrepeating units derived from methyl (meth)acrylate; (2) a copolymerhaving repeating units derived from urethane (meth)acrylate obtained bythe reaction of 2-hydroxyethyl (meth)acrylate with tolylenediisocyanate, repeating units derived from butyl (meth)acrylate,repeating units derived from 2-ethylhexyl (meth)acrylate, and repeatingunits derived from ethyl (meth)acrylate; and (3) a copolymer havingrepeating units derived from urethane (meth)acrylate obtained by thereaction of 2-hydroxyethyl (meth)acrylate with tolylene diisocyanate andrepeating units derived from ethyl (meth)acrylate.

Besides the above, the polymer having repeating units derived from anacrylic ester and/or a methacrylic ester used in the present inventionmay be copolymerized with a monomer having a functional group as far asthe amount of contained free organic acids, the total amount of theextracted acetic acid and formic acid, and appropriate adhesionproperties are not adversely affected. Example of monomers having afunctional group include a monomer having a hydroxyl group such as2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and allylalcohol; a monomer having an amide group such as (meth) acrylamide,N-methyl (meth)acrylamide, and N-ethyl (meth)acrylamide; a monomerhaving an amide group such as N-methylol (meth) acrylamide, anddimethylol (meth)acrylamide, and a methylol group; a monomer having afunctional group such as a monomer having an amino group such asaminomethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, andvinylpyridine; a monomer having an epoxy group such as allyl glycidylether, and glycidyl ether (meth)acrylate. Besides these monomers,fluorine-substituted (meth)acrylic acid alkyl ester,(meth)acrylonitrile, a vinyl group-containing aromatic compound such asstyrene and methylstyrene, vinyl acetate, and a halogenated vinylcompound are included.

Besides the aforementioned monomers having a functional group, theacrylic adhesive used in the present invention may be copolymerized withother monomers having an ethylene double bond. Examples of the monomershaving an ethylene double bond include α,β-unsaturated dibasic aciddiesters such as dibutyl maleate, dioctyl maleate, and dibutyl fumarate;vinyl ether; a vinyl aromatic compound such as styrene, α-methylstyreneand vinyl toluene; and (meth)acrylonitrile.

Besides the aforementioned monomers having an ethylene double bond, acompound having two or more ethylene double bonds may be used incombination. Examples of such compounds include divinylbenzene, diallylmaleate, diallyl phthalate, ethylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, methylene bis(meth)acrylamide.

In the polymer having repeating units derived from an acrylic esterand/or a methacrylic ester used for the adhesive layer of the presentinvention, the ratio of repeating units derived from one or two or morekinds of acrylic esters and/or methacrylic esters to the total number ofrepeating units of all monomers in a copolymer is preferably 50 mol % ormore, more preferably 80 mol % or more, still more preferably 90 mol %or more. A copolymer comprising only repeating units derived from two ormore kinds of acrylic esters and/or methacrylic esters is also suitablyused.

As a commercial product of the resin film having an adhesive layercontaining a polymer having repeating units derived from an acrylicester and/or a methacrylic ester, for example, C-200 and C-300 (productname; manufactured by: Nitto Denko Corporation); A-1330 (product name;manufactured by: Hitachi Chemical Co., Ltd.) are suitably used.

The adhesive layer of the present invention may contain an antioxidant,a curing agent (a cross-linking agent) such as an isocyanate compound orthe like, a tackifier, a silane coupling agent, a filler, and so on ifrequired as far as the effects of the present invention can be obtained.

The thickness of the adhesive layer of the protective film of thepresent invention is not particularly limited as far as it isappropriately determined in order to appropriately control the adhesionproperties of the adhesive layer with respect to thecopper-mesh-layer-side surface of the electromagnetic wave shieldingsheet. In general, the thickness of the adhesive layer is from 2 to 10μm.

As a measure of the adhesion of the adhesive layer of the protectivefilm of the present invention to the electromagnetic wave shieldingsheet, the delamination resistance of the adhesive layer evaluated inthe following manner is preferably from 0.05 to 1.3 N/25 mm. It ismeasured in such a manner that by means of a roller the adhesive layerof the protective film is allowed to adhere to non-mesh forming portionof a surface of an electrolytic copper foil having a thickness of 11 μm(product name: TC; manufactured by: Furukawa Circuit Foil Co., Ltd.), inwhich the surface has a “Rz JIS” (JIS B0601 (1994)) from 3 to 4.3 μm anda center line average roughness “Ra” (JIS B0601 (1994)) of fineirregularities on which part of the surface from 0.2 to 0.6 μm; theresulting sheet is cut to a size of 150 mm long by 25 mm wide; and theprotective film was measured using a tensile testing machine such as“Tensilon” (product name; manufactured by: Toyo Seiki Seisaku-sho, Ltd.)by stretching the protective film and the electrolytic copper foilsurface in a direction such that they make an angle of 180° at a pullingspeed of 300 mm/min and in an environment of 20 to 25° C.

(Release Layer)

The protective film of the present invention may further have a releaselayer so that during storage the adhesive layer does not adhere to thesupport surface on which no adhesive layer is laminated and can bestored in rolled or stacked form. The release layer may be laminated onthe support surface on which no adhesive layer is laminated. Moreover,the release layer may be laminated to the adhesive layer until theprotective film for temporary lamination to an electromagnetic waveshielding sheet is actually and temporarily laminated to theelectromagnetic wave shielding sheet. An easily peelable PET filmsubjected to a silicone treatment, for example, is suitably used as therelease layer. An easily peelable paper may be the release layer that islaminated on the adhesive layer until the protective film for temporarylamination to an electromagnetic wave shielding sheet is actually andtemporarily laminated to the electromagnetic wave shielding sheet.

(Method for Producing Protective Film)

The method for producing the protective film for temporary lamination toan electromagnetic wave shielding sheet of the present invention is amethod for producing a protective film for temporary lamination to acopper-mesh-layer-side surface of an electromagnetic wave shieldingsheet in which at least the copper mesh layer is provided on one surfaceof a transparent substrate, the method comprising the steps of:selecting an adhesive in which an amount of free organic acids is anamount that makes 10 or less a color difference ΔE_(L*a*b*) of thecopper-mesh-layer-side surface of the electromagnetic wave shieldingsheet before and after the adhesive is laminated on thecopper-mesh-layer-side surface and they are left for 200 hours in anatmosphere of a temperature of 60° C. and a relative humidity of 95%,from adhesives containing a polymer having repeating units derived froman acrylic ester and/or a methacrylic ester, and therewith forming anadhesive layer on a support.

Such a production method enables to produce a protective film thatleaves no adhesive residue behind when peeled off and causes no partialpeeling of a blackened layer and the like even in the case where theblackened layer and the like are further laminated on the copper meshlayer, while having appropriate adhesion properties that involves easyadhesion and easy peelability in a balanced manner with respect to acopper mesh layer of the electromagnetic wave shielding sheet; moreover,the protective film causes no discoloration of the electromagnetic waveshielding sheet even after long-term use, especially at high temperatureand high humidity.

B. Electromagnetic Wave Shielding Sheet

Now, the electromagnetic wave shielding sheet of the present inventionis described.

The first electromagnetic wave shielding sheet of the present inventionis an electromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of thetransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises asupport and an adhesive layer containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester on thecopper-mesh-layer-side surface of the support, and an amount of freeorganic acids in the adhesive layer is an amount that makes 10 or less acolor difference ΔE_(L*a*b*) of the copper-mesh-layer-side surface ofthe electromagnetic wave shielding sheet before and after the adhesivelayer surface is laminated on the copper-mesh-layer-side surface andthey are left for 200 hours in an atmosphere of a temperature of 60° C.and a relative humidity of 95%.

The second electromagnetic wave shielding sheet of the present inventionis an electromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of thetransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises anadhesive layer containing a polymer having repeating units derived froman acrylic ester and/or a methacrylic ester; the protective film istemporarily laminated to the copper-mesh-layer-side surface through theadhesive layer; and 20 ng/cm² or less is a total amount of acetic acidand formic acid extracted upon testing the protective film by a testmethod in which the adhesive layer surface of the protective film isextracted at 23° C. for 15 minutes with ultrapure water and theresulting extract is measured for an amount of extracted acetic acid andan amount of extracted formic acid by ion chromatography.

The third electromagnetic wave shielding sheet of the present inventionis an electromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of atransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises anadhesive layer containing a polymer having repeating units derived fromurethane acrylate and/or urethane methacrylate.

Temporarily laminating a temporary protective film to a copper meshlayer surface after forming the copper mesh layer surface on atransparent substrate by etching or plating has advantages such thatduring the time until the next process, the concave portion of theconductive mesh layer can be kept free of dust and the mesh lines can befree from contamination upon handling or storage. In the case oftemporarily laminating a film having an adhesive layer to a copper meshlayer, however, some adhesives cause problems such that adhesive residueis left behind when a temporarily laminated protective film is peeledoff and a blackened layer and the like are partially peeled off togetherwith the protective film if the blackened layer and the like are furtherlaminated on the copper mesh layer. An other problem is that the coppermesh layer discolors after the electromagnetic wave shielding sheet isstored for a long time, especially at high temperature and highhumidity.

In this regard, according to the present invention, since the protectivefilm uses an adhesive layer containing a polymer having repeating unitsderived from an acrylic ester and/or a methacrylic ester, especially apolymer having repeating units derived from urethane acrylate and/orurethane methacrylate for the adhesive to form an adhesive layer, theprotective film leaves no adhesive residue behind when peeled off andcauses no partial peeling of a blackened layer and the like that arefurther laminated on the copper mesh layer. In addition, the protectivefilm has good adhesion and removability.

Further, since the amount of free organic acids in the adhesive layer ofthe protective film is an amount that makes 10 or less the colordifference ΔE_(L*a*b*) of the copper-mesh-layer-side surface before andafter the above-specified test in a high temperature and high humidityenvironment, or since 20 ng/cm² or less is the total amount of aceticacid and formic acid extracted upon testing the protective film by theabove-specified test method, an electromagnetic wave shielding sheetthat does not discolor even after long-term use, especially at hightemperature and high humidity, can be obtained.

It appears that due to the same reasons as in “A. Protective film fortemporary lamination to electromagnetic wave shielding sheet,” theprotective film used in the present invention does not discolor evenafter long-term use, especially at high temperature and high humidity,while the copper mesh layer and the protective film exhibit appropriateadhesion properties.

(Layer Configuration)

FIGS. 2A to 2C are a sectional view of the electromagnetic waveshielding sheet of the present invention, showing an example of a basicembodiment.

FIG. 2A shows the configuration of an electromagnetic wave shieldingsheet 100 in which a copper mesh layer 14 is formed on a transparentsubstrate 11 and a protective film 10 provided with an adhesive layer 2and a support 1 is temporarily laminated to the copper mesh layer 14surface through the adhesive layer 2.

An electromagnetic wave shielding sheet may be further provided withother layers. In the electromagnetic wave shielding sheet of the presentinvention, from the viewpoint of improving visibility of a display imageby reducing light reflectance and enhancing contrast, a blackened layer17 is preferably provided on the copper mesh layer 14 as shown in FIG.2B.

In the configuration of FIGS. 2A and 2B, the copper mesh layer 14 may belaminated on the transparent substrate 11 through an adhesive layer (notshown.)

FIG. 2C shows an example of a layer configuration of an electromagneticwave shielding sheet in the case where the electromagnetic waveshielding sheet is formed by an electrolytic plating method, in whichconfiguration a conductive treating layer 13 is formed on thetransparent substrate 11, the copper mesh layer 14 and the blackenedlayer 17 are further laminated thereon in this sequence, and theprotective film 10 provided with the adhesive layer 2 and the support 1is temporarily laminated to the blackened layer 17 surface through theadhesive layer 2.

FIG. 3 is a perspective view only showing the transparent substratelayer 11, the conductive treating layer 13 and the copper mesh layer 14of the electromagnetic wave shielding sheet in FIG. 2C. The conductivetreating layer 13 and the copper mesh layer 14 (herein after, the bothlayers and other conductive layers are correctively referred to as a“conductor layer 12”) are in the form of a mesh with densely alignedopenings 103. The mesh 101 consists of a combination of mesh lines 104and openings 103. The blackened layer 17 (not shown) that is furtherlaminated on the copper mesh layer 14 is incorporated with the conductorlayer 12 to form the mesh 101.

FIG. 4A is a sectional view taken along the line A-A of FIG. 3. FIG. 4Bis a sectional view taken along the line B-B of FIG. 3. FIG. 4A shows asection of the openings, in which the openings 103 and the mesh lines104 are formed alternately. FIG. 4B shows a section of the mesh line104, in which the mesh line 104 comprising the copper mesh layer 14 andthe conductive treating layer 13 is continuously formed. The sectionalviews of the electromagnetic wave shielding sheet of FIGS. 2A to 2Ccorrespond to a sectional view taken along to the line A-A.

The embodiments of the electromagnetic wave shielding sheet of thepresent invention are not limited by the above-mentioned examples. Asfar as the protective film is laminated with its adhesive layer to thecopper-mesh-layer-side surface of an electromagnetic wave shieldingsheet, other protective films may be further laminated to thetransparent substrate surface on which no copper mesh layer is laminatedof the electromagnetic wave shielding sheet. The electromagnetic waveshielding sheet of the present invention may be in a form such thatsingle- or multi-layered optical filters are preliminarily laminated tothe transparent substrate surface on which no copper mesh layer islaminated of the electromagnetic wave shielding sheet. Examples of theoptical filters include, for example, an antireflection layer, anear-infrared absorbing layer, and an anti-glare layer. Any that has thesubstantially same essential features as the technical ideas describedin claims of the present invention and exerts the same effects andadvantages is included in the technical scope of the present invention.

Hereinafter, layers of the electromagnetic wave shielding sheet of thepresent invention will be described, starting from a transparentsubstrate. The same protective film as the above-mentioned one of thepresent invention may be used for the protective film of theelectromagnetic wave shielding sheet of the present invention. Thus, anexplanation for the protective film of the electromagnetic waveshielding sheet of the present invention is omitted herein.

(Transparent Substrate)

A transparent substrate is a layer to reinforce a copper mesh layer withlow mechanical strength. Accordingly, with appropriate consideration ofheat resistance properties, insulation properties and so on, one withmechanical strength and optical transparency may be selected to usedepending on the application. Specific Examples of the transparentsubstrate include, for example, a plate and a sheet (or film) made oforganic material such as resin, and a plate made of inorganic materialsuch as glass.

Examples of transparent resins used for the above-mentioned plate andsheet of organic material include, for example, polyester resins such aspolyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, a copolymer of terephthalic acid, isophthalic acid andethylene glycol, a copolymer of terephthalic acid, cyclohexanedimethanoland ethylene glycol, polyamide resins such as such as nylon 6,polyolefin resins such as polypropylene and polymethylpentene, acrylicresins such as polymethylmethacrylate, styrene resins such aspolystyrene, a copolymer of styrene and acrylonitrile, cellulose resinsuch as triacetyl cellulose, imide resins, and polycarbonate resins.

As a resin material, these resins are used solely or in combination(i.e. a mixed resin or a polymer alloy.) They are used as a single layeror a laminate composed of multiple layers. In the case where they areused as a resin sheet, they are preferably used as a uniaxially orientedsheet or a biaxially oriented sheet from the viewpoint of mechanicalstrength.

The resins may appropriately contain an additive such as an ultra violetabsorber, a filler, a plasticizer, an antistatic agent as needed.

Examples of the glass used for the above-mentioned glass plate includequartz glass, borosilicate glass, and soda-lime glass. Alkali-free glassor the like is more preferable, which has a low thermal expansioncoefficient, is excellent in dimensional stability and workability atheat-treatment at an elevated temperature, and contains no alkalinecomponent. A glass plate of such a glass may be used at the same time asan electrode substrate that will be used as a front substrate of adisplay.

The thickness of the transparent substrate is not particularly limitedand may be determined according to the application. In the case of atransparent substrate made of a transparent resin, the thickness isgenerally from 12 to 1,000 μm, more preferably from 50 to 500 μm. If atransparent substrate is a glass plate, a glass plate having a thicknessfrom 1 to 5 mm is generally preferable. Any of the materials having athickness less than the range is insufficient in mechanical strength soas to cause warpage, loosening or breaking. Any of the materials havinga thickness exceeding the range is excess in performance and expensive;moreover, thinning the electromagnetic wave shielding sheet becomesdifficult.

The transparent substrate may be used as a front substrate that is acomponent of a display device comprising a front substrate and a backsubstrate. In the embodiment in which the electromagnetic wave shieldingsheet is used as a front filter to be disposed in front of a frontsubstrate, a sheet is more excellent than a plate in terms of thinnessand lightness. In terms of durability, a resin sheet is more excellentthan a glass plate.

For the above-mentioned reasons, a resin sheet is a preferred materialfor a transparent substrate. Among resin sheets, a polyester resin sheetof, for example, polyethylene terephthalate or polyethylene naphthalateis particularly preferable in terms of transparency, heat resistance,costs, and so on. Further, a biaxially oriented polyethyleneterephthalate sheet is most preferable. Higher transparency is betterfor the transparent substrate, and an optical transparency having avisible light transmission of 80% or more is preferable.

A conventionally known adhesion-enhancing treatment such as a coronadischarge treatment, a plasma treatment, an ozone treatment, a flametreatment, a primer treatment, a preheating treatment, a dust removaltreatment, a vapor deposition treatment, and an alkali treatment may beappropriately performed on the surface of the transparent substrate.

(Copper Mesh Layer)

The copper mesh layer is a conductive layer that functions to shieldelectromagnetic waves. The copper mesh layer itself is non-transparent;however, it involves electromagnetic wave shielding properties andoptical transparency in a balanced manner since it is in the form of amesh and provided with openings.

A layer that is conductive and functions to shield electromagnetic wavesmay consist of a copper mesh layer only or a combination of a coppermesh layer and other layers of conductive materials. Examples of theother layers of conductive materials include, for example, a thinconductive layer which is to be used as a base layer for copper plating(herein after referred to as a conductive treating layer) and aconductive blackened layer, and they are collectively referred to as aconductor layer. In FIG. 2C, for example, if the blackened layer 17 isconductive, a conductor layer means the conductive treating layer 13,the copper mesh layer 14 and the blackened layer 17. If the blackenedlayer 17 is not conductive, a conductor layer means the conductivetreating layer 13 and the copper mesh layer 14.

The copper mesh layer of the invention is a mesh layer containingcopper. Examples of the copper mesh layer of the present inventioninclude a mesh layer made of a copper alloy such as brass, bronze,phosphor bronze, cupronickel, and phosphorus-containing copper.

The conductor layer including the copper mesh layer may be any shape andthere is no particular limit. The opening is typically square-shaped.The opening may be in a polygonal shape including a triangular shapesuch as an equilateral triangular shape, a quadrangular shape such as asquare shape, a rectangular shape, a diamond shape, a trapezoidal shape,a hexagonal shape; or in a spherical shape or an ellipsoidal shape. Themesh has multiple openings in any of the above-mentioned shapes so as tobe formed into a grid of lines between the openings, each of which linesgenerally has a uniform width. In general, the openings and the meshlines of the entire copper mesh layer are the same in shape and size,respectively. More specifically, in consideration of the aperture ratioand the non-visibility of the mesh, the width of the mesh lines 104between the openings (i.e., the line width “W”) is preferably 40 μm orless, more preferably 20 μm or less. However, in order to exhibit theelectromagnetic wave shielding effect and prevent breaking, it ispreferable for the mesh lines to ensure a line width of at least 5 μm ormore. The width of the openings can be represented by: (the line pitch“P”)-(the line width “W”), and it is preferably 150 μm or more, morepreferably 200 μm or more in the present invention in terms of opticaltransparency and that air bubbles hardly remain in the openings whenlaminated to an optical filter as will be described below. In order toexhibit the shielding effect of electromagnetic waves in the range ofMHz to GHz, it has to be 3,000 μm at the maximum.

The height of the mesh lines 104 is approximately from 1 to 100 μm,preferably from 2 to 20 μm. If the thickness is far less than the range,the electrical resistance increases so that it becomes difficult toobtain a sufficient electromagnetic wave shielding performance. If thethickness exceeds the range, it becomes difficult to obtain a highlyprecise mesh pattern so that the uniformity of the mesh patterndecreases. The height of the mesh lines is the total thickness of, amongthe conductor layer 12 and non-conductive layers that are furtherlaminated on the conductor layer 12, all layers which are provided withthe openings and thus form the mesh lines 104. The bias angle of themesh, which is an angle made by the meeting of the mesh lines of themesh and the outer periphery of the electromagnetic wave shieldingsheet, may be appropriately set at an angle that hardly produces moirepatterns, in consideration of the pixel pitch or light emissionproperties of a display.

The method for forming the copper mesh layer is not particularlylimited. Various conventionally known methods of forming an opticallytransparent electromagnetic wave shielding sheet may be appropriatelyemployed, including the following four methods for example.

(1) A method in which a pattern is printed on a transparent substratewith an electric conductive ink, and a metal plating is applied on theelectric conductive ink layer (see, for example, JP-A 2000-13088.)

(2) A method in which an electric conductive ink or a photosensitivecoating liquid containing a catalyst for chemical plating is entirelyapplied on a transparent substrate, the applied layer is formed into amesh by a photolithography method, and a metal plating is applied on themesh (see, for example, “Photosensitive Catalyst for Electro-lessPlating with Fine Pattern”, Advanced Materials Research Group NewTechnology Research Laboratory Sumitomo Osaka Cement Co., Ltd., onSumitomo Osaka Cement Co., Ltd. Web Page,http://www.socnb.com/product/hproduct/display.html, accessed on Jan. 7,2003.)

(3) A transparent substrate is laminated to a metal foil with anadhesive, and then the metal foil is formed into a mesh by aphotolithography method (see, for example, JP-A 11-145678.)

(4) A transparent substrate is prepared in which a metal thin film isformed by sputtering or the like on one surface of the transparentsubstrate to form a conductive treating layer and on the conductivetreating layer a metal layer is formed by electrolytic plating as ametal plating layer. The metal plating layer of the metal platingtransparent substrate and the conductive treating layer are formed to bemesh like by a photolithography method (see, for example, JapanesePatent No. 3502979, JP-A 2004-241761.)

(Blackened Layer)

In order to absorb outside light incident on the electromagnetic waveshielding sheet and improve the visibility of an image on a display, ablackened layer is preferably provided on the electromagnetic waveshielding sheet of the present invention in terms of enhancing contrast.Some blackened layer can increase adhesion due to its rough surface.

The blackened layer may be a layer which is in dark color such as blackand satisfies the basic properties such as adhesion, and conventionallyknown blackened layers may be appropriately used. The blackened layer isnot necessarily required to have conductivity.

Consequently, inorganic materials such as metal or organic materialssuch as black-colored resin may be used to form the blackened layer.

In the case of using inorganic materials, a metallic layer of a metal,an alloy, a metallic compound such as a metal oxide or metal sulfide isformed as the blackened layer. As a method for forming a metallic layer,various conventionally known blackening treatments may be appropriatelyused. Especially, blackening treatment by a plating method is preferablyin terms of adhesiveness, uniformity, and simplicity. Materials used forplating include, for example, metals such as copper, cobalt, nickel,zinc, molybdenum, tin and chromium, and metallic compounds. Plating withthese materials is more excellent than using cadmium or the like forplating in terms of adhesiveness, blackness and so on.

Materials including Black chromium, black nickel (nickel sulfide) andnickel alloys are preferably used to form the blackened layer. Thenickel alloys include an alloy of nickel and zinc, an alloy of nickeland tin, and an alloy of nickel, tin and copper. In general, particlesof the blackened layer are needle shaped so that they are easilydeformed by external force and change their appearance. A blackenedlayer of a nickel alloy has advantages such that particles are hardlydeformable and their appearance hardly changes in a post-process. In thecase of using a blackened layer of nickel sulfide, there is an advantageof high productivity. In this case, however, there is a problem thatdiscoloration of the blackened layer can easily occur due to an adhesiveof the protective layer. The present invention can solve the problem.When a nickel alloy is used as the material of a blackened layer, themethod for forming the blackened layer may be a conventionally knownelectrolytic or electroless plating. A nickel alloy may be formed afterconducting a nickel plating.

Plating methods suitable as a blackening treatment include a cathodicelectrodeposition plating method in which a conductor layer of copper issubjected to cathodic electrolysis in an electrolyte of such as sulfuricacid, copper sulfate, or cobalt sulfate, thereby depositing cationicparticles on the conductor layer. According to this method, the cationicparticles deposited on the conductor layer blacken the conductor layerand at the same time roughen the surface of the conductor layer. As thecationic particles, particles of copper or copper-alloy may be used. Asthe particles of copper alloy, copper and cobalt alloy particles arepreferable. The average particle diameter of the alloy particles ispreferably from 0.1 to 1 μm. By using copper and cobalt alloy particles,a blackened layer comprising a copper-cobalt alloy particle layer can beobtained. The cathodic electrodeposition plating method is alsopreferable in terms that the average particle diameter of cationicparticles to be deposited can be controlled from 0.1 to 1 μm. If theaverage particle diameter exceeds the range, the density of thedeposited particles decreases. Thus, the blackness of the blackenedlayer decreases, becomes uneven, and detachment of the particles mayeasily occur. On the other hand, even if the average particle diameteris less than the range, the blackness of the blackened layer decreases.When conducting the cathodic electrodeposition at high current density,the surface of the copper mesh layer becomes cathodic and is activatedby reducing hydrogen so that significantly improved adhesion can beobtained between the copper surface and the cationic particles.

The black density of the blackened layer is preferably 0.6 or more.Measurement of black density is carried out by means of COLOR CONTROLSYSTEM GRETAG SPM100-11 (product name; manufactured by: Kimoto Co.,Ltd.) with an angle of observation field of 100 and observation lightsource D50. Illumination type is set to density standard ANSIT. Aspecimen is subject to measurement after white calibration. The lightreflectance of the blackened layer is preferably 5% or less. Lightreflectance is measured by means of Haze Meter HM150 (product name;manufactured by: Murakami Color Research Laboratory Co., Ltd.) inaccordance with JIS-K7105, or it may be expressed by a reflectance value“Y” using a color-difference meter. In this case, “Y” is preferably 15or less.

In the electromagnetic wave shielding sheet of the present invention,surface roughness of the copper-mesh-layer-side surface to which theprotective film is temporarily laminated is preferably a ten-pointaverage roughness “Rz JIS” (JIS B0601 (1994)) of the profile from 0.5 to5.0 μm when a roughness profile is used as a profile of the surface, anda center line average roughness “Ra” (JIS B0601 (1994)) of fineirregularities on the surface from 0.1 to 3.0 μm from the viewpoint thatthe protective film can have adhesion and removability of the protectivefilm when combined with an adhesive specified in the present invention,that is, the protective film leaves no adhesive residue behind whenpeeled off and causes no partial peeling of a blackened layer and thelike if the blackened layer and the like are further laminated on thecopper mesh layer.

(Lamination of Protective Film)

There is no particular limit to the method for temporarily laminatingthe above-mentioned protective film to a copper-mesh-layer-side surfaceof the electromagnetic wave shielding sheet in which at least the coppermesh layer is provided on one surface of a transparent substrate.

Any laminator such as a roll laminator or a flat bed laminator may beused as far as it can apply pressure to an optical filter and anelectromagnetic wave shielding sheet. A roll laminator is preferablesince it corresponds to roll to roll lamination method and enablescontinuous production.

Lamination pressure is not particularly limited. For example, in thecase of using a roll laminator, a linear pressure from 1 to 20 kgf/cm ispreferable. The temperature of a pressure member of a laminator is notparticularly limited.

FIG. 5 shows an example of a process for laminating an electromagneticwave shielding sheet to a protective film by means of a laminator. Aroll of an electromagnetic wave shielding sheet is set in a first paperfeed member 21 of a laminator. A roll of a laminate sheet comprising arelease film and a protective film (an adhesive layer and a support) isset in a second paper feed member 22. While the electromagnetic waveshielding sheet is fed from the first paper feed member 21, the laminatesheet is fed from the second paper feed member 22. At the same time, therelease film is wound up onto a wind-up roller 24. A copper mesh layerside of the electromagnetic wave shielding sheet and the adhesive layerside of the protective film are faced to each other. They are laminatedto each other by means of a first laminating unit 25 at a laminationpressure of approximately 10 kgf/cm, and then again by a secondlaminating unit 26 at a lamination pressure of approximately 10 kgf/cm.The lamination result is wound onto a wind-up roll 27, thus obtaining alaminate sheet comprising the electromagnetic wave shielding sheet andthe protective film (the adhesive layer and the support.) Two laminatingunit are used in FIG. 5; however, only one laminating unit may be usedto laminate if it can provide a good lamination result.

The electromagnetic wave shielding sheet with the protective film of thepresent invention may be distributed in the form of a continuous band(roll) or separate sheets. There is no particular limit to the means forseparating the sheet into separate sheets. Any kind of cutting means forfilters may be used.

As described above, the protective film for temporary lamination to anelectromagnetic wave shielding sheet of the present invention canprovide an effect that the protective film leaves no adhesive residuebehind when peeled off and causes no partial peeling of a blackenedlayer and the like even in the case where the blackened layer and thelike are further laminated on the copper mesh layer, while havingappropriate adhesion properties that involves easy adhesion and easypeelability in a balanced manner with respect to a copper mesh layer ofthe electromagnetic wave shielding sheet. Especially, if the amount of aspecific acid in the adhesive layer is less than the specified amount,the protective film provides an additional effect that if causes nodiscoloration of the electromagnetic wave shielding sheet even afterlong-term use, especially at high temperature and high humidity.

The electromagnetic wave shielding sheet of the present invention is anelectromagnetic wave shielding sheet with a protective film that istemporarily laminated on a copper mesh layer for shieldingelectromagnetic waves, which sheet provides an effect that theprotective film leaves no adhesive residue behind when peeled off andcauses no partial peeling of a blackened layer and the like even in thecase where the blackened layer and the like are further laminated on thecopper mesh layer, while the copper mesh layer and the protective filmexhibit easy adhesion and easy peelability. Especially, if the amount ofa specific acid in the adhesive layer of the protective film is lessthan the specified amount, the protective film provides an additionaleffect that if causes no discoloration of the copper mesh layer evenafter long-term use, especially at high temperature and high humidity.

The method for producing the protective film for temporary lamination toan electromagnetic wave shielding sheet of the present invention canprovide effects that can obtain the protective film, in which theprotective film leaves no adhesive residue behind when peeled off andcauses no partial peeling of a blackened layer and the like even in thecase where the blackened layer and the like are further laminated on thecopper mesh layer, while having appropriate adhesion properties thatinvolves easy adhesion and easy peelability in a balanced manner withrespect to a copper mesh layer of the electromagnetic wave shieldingsheet; moreover, the protective film causes no discoloration of theelectromagnetic wave shielding sheet even after long-term use,especially at high temperature and high humidity.

The present invention is not limited by the above-mentioned embodiments.The above-mentioned embodiments are examples, and any that has thesubstantially same essential features as the technical ideas describedin claims of the present invention and exerts the same effects andadvantages is included in the technical scope of the present invention.

EXAMPLES

Hereinafter, the present invention will be explained further in detailwith reference to examples. The scope of the present invention may notbe limited to the following examples. Herein, “part(s)” refers to“part(s) by weight” if not particularly mentioned.

(Tests)

Each of the adhesive layer surfaces of the following protective films“A” to “D” was extracted at 23° C. for 15 minutes with ultrapure water.In particular, each protective film was cut into a size of 10 cm×10 cmand the adhesive layer of the cut out film was entirely immersed in 500ml of ultrapure water and left at 23° C. for 15 minutes while.

The amounts of acetic acid and formic acid were measured for theresulting extract of each cut out film by ion chromatography. Saidextraction was performed in a clean booth with a chemical filter. Theelution amount (ng/cm²) of each component per unit area was obtained bymultiplying the concentration of acetic acid/forming acid in theresulting extract (ng/mL) by the amount of the resulting extract (mL)and then dividing the result by the extraction area (cm².)

Protective film A: An adhesive layer of the protective film A comprisesan acrylic copolymer formed by copolymerizing urethane methacrylate,which is obtained by reaction of 2-hydroxyethyl methacrylate withtolylene diisocyanate, with methyl methacrylate. The thickness of theadhesive layer is 6 μm. The total thickness of the protective film A is60 μm.

Protective film B: An adhesive layer of the protective film B comprisesan acrylic copolymer formed by copolymerizing urethane methacrylate,which is obtained by reaction of 2-hydroxyethyl methacrylate withtolylene diisocyanate, with butyl acrylate, 2-ethylhexyl acrylate, andethyl acrylate. The thickness of the adhesive layer is 6 μm. The totalthickness of the protective film B is 60 μm.

Protective film C: An adhesive layer of the protective film C comprisesan acrylic polymer formed by copolymerizing butyl acrylate with2-ethylhexyl acrylate. The thickness of the adhesive layer is 6 μm. Thetotal thickness of the protective film C is 60 μm.

Protective film D: An adhesive layer of the protective film D comprisesa rubber copolymer comprising a styrene-isobutylene copolymer. Thethickness of the adhesive layer is 6 μm. The total thickness of theprotective film D is 60 μm.

Ion chromatography measurement condition was given as follows.

Apparatus: DX-600 (product name; manufactured by: Nippon Dionex K.K.)

Column: AG11-HC+AS11-HC

Eluent: KOH

Eluent concentration: 1 to 35 mM (Gradient)

(Test Results of the Amounts of Acetic Acid and Formic Acid) Table 1shows the amounts of acetic acid and formic acid obtained by themeasurement. It is thus found that the protective film A and theprotective film B could be used as the protective film for temporarylamination to an electromagnetic wave shielding sheet of the presentinvention.

TABLE 1 Extracted Amount of Each Acid per Unit Area (ng/cm²) Acetic AcidFormic Acid Protective Film A 1.2 0.7 Protective Film B 1.6 1.1Protective Film C 86 16 Protective Film D Below Below detectabledetectable limit limit

Example 1

An electromagnetic wave shielding sheet 100 shown in FIG. 2C wasproduced as follows.

As a transparent substrate 11, a color less, transparent,biaxially-stretched polyethylene terephthalate film in the form of acontinuous belt was prepared. The polyethylene terephthalate film had athickness of 100 μm and a polyester resin primer layer on one surfacethereof.

On the primer layer of the transparent substrate, a 0.1 μm thicknickel-chromium alloy layer and a 0.2 μm thick copper layer wereprovided in this sequence by a sputtering method so as to prepare aconductive treating layer 13.

On the conductive treating layer surface, a 2.0 μm thick copper platedlayer 15 was provided by an electrolytic plating method using a coppersulfate bath (herein after, the conductive treating layer 13 and thecopper plated layer are referred to as a metal layer 18 in combination.)As a result of forming the metal layer 18 on the transparent substrate,there was produced a copper-clad laminate sheet 20 as shown in FIG. 6A,in which the metal layer 18 was directly formed on the transparentsubstrate without an adhesive layer in between.

Next, the laminate sheet 20 was etched using the photolithographicmethod for the conductor layer 12 to form a mesh comprising openings 103and mesh lines 104 as shown in FIG. 6B, thereby obtaining a laminate 30.

In etching, using a production line for a color TV shadow mask, aprocess from masking to etching was consistently performed on thecontinuous belt-shaped laminate sheet. A photosensitive etching resistwas applied to the entire surface of the conductor layer surface of thelaminate sheet and then a desired mesh pattern was transferred bycontact exposure, followed by development, film-hardening treatment, andbaking, so that the resist layer was patterned such that the resistlayer remains on portions corresponding to mesh lines and no resistlayer remains on portions corresponding to openings of the mesh. Next,the conductor layer was etched and removed in an aqueous ferric chlorideto form mesh openings, followed by water washing, resist stripping,cleaning and drying in this sequence.

The mesh pattern of the mesh area had square openings and mesh lineshaving a line width of 10 μm, a line distance (pitch) of 300 μm, and aline height of 2.3 μm. When the mesh is cut in the form of a rectangularsheet, the bias angle, which is defined as an inferior angle to the longside of the rectangular sheet, is 49 degrees.

Next, a blackened layer 17 was formed on a metal layer 18 of thelaminate 30. In particular, using a nickel plate as an anode, thelaminate sheet in which the mesh-shaped conductor layer was formed onthe transparent substrate was immersed in a plating bath of a mixture ofa nickel ammonium sulfate solution, a zinc sulfate solution, and asodium thiocyanate solution for a blackening treatment. The exposedsurface of the conductor layer was entirely covered with the blackenedlayer 17 made of a nickel-zinc alloy, thus obtaining a laminate 40 asshown in FIG. 6C, in which the conductor layer 12 comprising theconductive treating layer 13, the copper mesh layer 14, and theblackened layer 17 was laminated.

To the copper mesh side of the laminate 40, using a roll laminator, theprotective film A in which an acrylic adhesive layer was laminated to a50 μm thick polyethylene film support was laminated by pressing thembetween a pair of pressure rollers comprising a rubber coated steelcore, at a roller pressure (total pressure) of 0.2 MPa and a processingspeed of 15 meters per minute, thus producing an electromagnetic waveshielding sheet 100 of Example 1 as shown in FIG. 6D, having a structurecomprising: the transparent substrate, the conductor layer 12(comprising the conductive treating layer 13, the copper mesh layer 14,and the blackened layer 17,) and a protective film A 10 (comprising theadhesive layer 2 and a polyethylene film 1) in sequence.

Example 2

An electromagnetic wave shielding sheet was produced as in Example 1,except that the protective film A was changed to the protective film B.

Comparative Example 1

An electromagnetic wave shielding sheet was produced as in Example 1,except that the protective film A was changed to the protective film C.

Comparative Example 2

An electromagnetic wave shielding sheet was produced as in Example 1,except that the protective film A was changed to the protective film D.

(Evaluation)

Examples and Comparative Examples were evaluated on the followingpoints. The results are shown in Table 2.

(1) Discoloration Property 1

Firstly, chromaticities a*, b*, and a luminance L* (defined by theInternational Commission on Illumination (CIE)) were measured for thecopper mesh side surface of the electromagnetic wave shielding sheets ofExamples and Comparative Examples. After the electromagnetic waveshielding sheets were exposed to an atmosphere of high temperature andhigh humidity (60° C., 95% RH) for 200 hours, chromaticities a*, b*, anda luminance L* were measured again for the copper mesh side surface ofthe electromagnetic wave shielding sheets. From results of themeasurements, a color difference ΔE before and after exposed to anatmosphere of high temperature and high humidity was obtained. In Table2, the marking “x” indicates ΔE_(L*a*b*)>10 (i.e., the case where acolor difference is above a narrow margin by visual examination anddiscoloration is clearly and visually observed.) The marking “Δ”indicates 1<ΔE_(L*a*b*)≦10 (i.e., the case where a color difference isbelow a narrow margin by visual examination.) The marking “o” indicatesΔE_(L*a*b*)≦1 (i.e., the case where a color difference is below adifferential threshold of discoloration by visual examination.)

(2) Discoloration Property 2

The electromagnetic wave shielding sheets were exposed to a dryatmosphere of high temperature (80° C.) for 200 hours to measurechromaticities a*, b*, and a luminance L of the copper mesh sidesurface. From results of the measurements, a color differenceΔE_(L*a*b*) was obtained. The color difference ΔE_(L*a*b*) of the coppermesh side surface of each electromagnetic wave shielding sheet wasevaluated in accordance with the standard mentioned in “(1)Discoloration property 1.”

(3) Delamination Resistance (Adhesion)

Each electromagnetic wave shielding sheet to which each correspondingprotective film was temporarily laminated was cut to a size of 150 mmlong by 25 mm wide. The cut-off protective film was measured using atensile tester (product name: Tensilon; manufactured by: Toyo SeikiSeisaku-sho, Ltd.) by stretching the protective film and thecopper-mesh-layer-side surface in a direction such that they make anangle of 180° at a stretching speed of 300 mm/min and in an atmosphereof a temperature from 20 to 25° C.

(4) Adhesive Residue

In the evaluation of delamination resistance, it was visually determinedif adhesive residue was left on the copper-mesh-layer-side surface ornot when the protective film was peeled off. The marking “o” indicatesthat no adhesive was left on the copper-mesh-layer-side surface, and “x”indicates that adhesive was left on the copper-mesh-layer-side surface.

(5) Peeling of Blackened Layer

In the evaluation of delamination resistance, it was visually determinedif partial peeling of the blackened layer occurred and the peelingadhered to the adhesive layer surface of the protective film when theprotective film was peeled off. The marking “o” indicates no peeling ofthe blackened layer occurred, and “x” indicates that part of theblackened layer was peeled off and adhered to the adhesive layersurface.

TABLE 2 Delamination Peeling of Protective Discoloration DiscolorationResistance Adhesive Blackened Film property 1 property 2 (N/25 mm)Residue Layer Example1 Protective ◯ ◯ 0.49 ◯ ◯ Film A Example2Protective ◯ ◯ 1.1 ◯ ◯ Film B Comparative Protective X X 0.69 ◯ ◯Example 1 Film C Comparative Protective ◯ ◯ 0.12 X X Example 2 Film D

(Results)

The above-described Examples and Comparative Examples result in thefollowing findings.

The electromagnetic wave shielding sheets of Examples 1 and 2 are suchthat the protective film left no adhesive residue behind when peeled offand caused no partial peeling of a blackened layer and the like thatwere further laminated on the copper mesh layer, while the copper meshlayer and the protective film exhibited appropriate easy adhesion andeasy peelability. Moreover, the electromagnetic wave shielding sheetsdid not discolor even after long-term use, especially at hightemperature and high humidity.

On the other hand, the electromagnetic wave shielding sheet ofComparative Example 1, in which the amounts of acetic acid and formicacid extracted from the adhesive layer were large, had adequate adhesionproperties; however, discoloration was observed after long-term storage,especially at high temperature and high humidity. In Comparative Example2 using a rubber adhesive layer, discoloration of the copper mesh wasnot a problem and in a favorable state; however, the protective filmleft adhesive residue behind and caused partial peeling of the blackenedlayer when peeled off.

1. A protective film for temporary lamination to an electromagnetic waveshielding sheet in which at least a copper mesh layer is provided on onesurface of a transparent substrate, wherein the protective film is fortemporary lamination to a copper-mesh-layer-side surface of theelectromagnetic wave shielding sheet, wherein the protective filmcomprises a support and an adhesive layer containing a polymer havingrepeating units derived from an acrylic ester and/or a methacrylic esteron the support, and wherein an amount of free organic acids in theadhesive layer is an amount that makes 10 or less a color differenceΔE_(L*a*b*) of the copper-mesh-layer-side surface of the electromagneticwave shielding sheet before and after the adhesive layer surface islaminated on the copper-mesh-layer-side surface and they are left for200 hours in an atmosphere of a temperature of 60° C. and a relativehumidity of 95%.
 2. The protective film for temporary lamination to anelectromagnetic wave shielding sheet according to claim 1, wherein therepeating units derived from an acrylic ester and/or a methacrylic esterin the adhesive layer comprise repeating units derived from urethaneacrylate and/or urethane methacrylate.
 3. A protective film fortemporary lamination to an electromagnetic wave shielding sheet, whereinthe protective film comprises a support and an adhesive layer containinga polymer having repeating units derived from an acrylic ester and/or amethacrylic ester on the support, and wherein 20 ng/cm² or less is atotal amount of acetic acid and formic acid extracted upon testing theprotective film by a test method in which the adhesive layer surface ofthe protective film is extracted at 23° C. for 15 minutes with ultrapurewater and the resulting extract is measured for an amount of extractedacetic acid and an amount of extracted formic acid by ionchromatography.
 4. The protective film for temporary lamination to anelectromagnetic wave shielding sheet according to claim 3, wherein therepeating units derived from an acrylic ester and/or a methacrylic esterin the adhesive layer comprise repeating units derived from urethaneacrylate and/or urethane methacrylate.
 5. A protective film fortemporary lamination to an electromagnetic wave shielding sheet, whereinthe protective film comprises a support and an adhesive layer containinga polymer having repeating units derived from urethane acrylate and/orurethane methacrylate on the support.
 6. An electromagnetic waveshielding sheet comprising: a transparent substrate; at least a coppermesh layer provided on one surface of the transparent substrate; and aprotective film temporarily laminated to a copper-mesh-layer-sidesurface, wherein the protective film comprises a support and an adhesivelayer containing a polymer having repeating units derived from anacrylic ester and/or a methacrylic ester on the copper mesh layer sideof the support, and wherein an amount of free organic acids in theadhesive layer is an amount that makes 10 or less a color differenceΔE_(L*a*b*) of the copper-mesh-layer-side surface of the electromagneticwave shielding sheet before and after the adhesive layer surface islaminated on the copper-mesh-layer-side surface and they are left for200 hours in an atmosphere of a temperature of 60° C. and a relativehumidity of 95%.
 7. The electromagnetic wave shielding sheet accordingto claim 6, wherein the repeating units derived from an acrylic esterand/or a methacrylic ester in the adhesive layer of the protective filmcomprise repeating units derived from urethane acrylate and/or urethanemethacrylate.
 8. The electromagnetic wave shielding sheet according toclaim 6, wherein delamination resistance of the adhesive layer of theprotective film is from 0.05 to 1.3 N/25 mm with respect to thecopper-mesh-layer-side surface.
 9. The electromagnetic wave shieldingsheet according to claim 6, wherein surface roughness of thecopper-mesh-layer-side surface to which the protective film istemporarily laminated is, when a roughness profile is used as a profileof the surface, a ten-point average roughness “Rz JIS” (JIS B0601(1994)) of the profile from 0.5 to 5.0 μm.
 10. The electromagnetic waveshielding sheet according to claim 6, wherein surface roughness of thecopper-mesh-layer-side surface to which the protective film istemporarily laminated is a center line average roughness “Ra” (JIS B0601(1994)) of fine irregularities on the surface from 0.1 to 3.0 μm.
 11. Anelectromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of thetransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises asupport and an adhesive layer containing a polymer having repeatingunits derived from an acrylic ester and/or a methacrylic ester on thesupport; the protective film is temporarily laminated to thecopper-mesh-layer-side surface through the adhesive layer; and 20 ng/cm²or less is a total amount of acetic acid and formic acid extracted upontesting the protective film by a test method in which the adhesive layersurface of the protective film is extracted at 23° C. for 15 minuteswith ultrapure water and the resulting extract is measured for an amountof extracted acetic acid and an amount of extracted formic acid by ionchromatography.
 12. The electromagnetic wave shielding sheet accordingto claim 11, wherein the repeating units derived from an acrylic esterand/or a methacrylic ester in the adhesive layer of the protective filmcomprise repeating units derived from urethane acrylate and/or urethanemethacrylate.
 13. The electromagnetic wave shielding sheet according toclaim 11, wherein delamination resistance of the adhesive layer of theprotective film is from 0.05 to 1.3 N/25 mm with respect to thecopper-mesh-layer-side surface.
 14. The electromagnetic wave shieldingsheet according to claim 11, wherein surface roughness of thecopper-mesh-layer-side surface to which the protective film istemporarily laminated is, when a roughness profile is used as a profileof the surface, a ten-point average roughness “Rz JIS” (JIS B0601(1994)) of the profile from 0.5 to 5.0 μm.
 15. The electromagnetic waveshielding sheet according to claim 11, wherein surface roughness of thecopper-mesh-layer-side surface to which the protective film istemporarily laminated is a center line average roughness “Ra” (JIS B0601(1994)) of fine irregularities on the surface from 0.1 to 3.0 μm.
 16. Anelectromagnetic wave shielding sheet comprising: a transparentsubstrate; at least a copper mesh layer provided on one surface of atransparent substrate; and a protective film temporarily laminated to acopper-mesh-layer-side surface, wherein the protective film comprises asupport and an adhesive layer containing a polymer having repeatingunits derived from urethane acrylate and/or urethane methacrylate on thecopper mesh layer side of the support.
 17. The electromagnetic waveshielding sheet according to claim 16, wherein delamination resistanceof the adhesive layer of the protective film is from 0.05 to 1.3 N/25 mmwith respect to the copper-mesh-layer-side surface.
 18. Theelectromagnetic wave shielding sheet according to claim 16, whereinsurface roughness of the copper-mesh-layer-side surface to which theprotective film is temporarily laminated is, when a roughness profile isused as a profile of the surface, a ten-point average roughness “Rz JIS”(JIS B0601 (1994)) of the profile from 0.5 to 5.0 μm.
 19. Theelectromagnetic wave shielding sheet according to claim 16, whereinsurface roughness of the copper-mesh-layer-side surface to which theprotective film is temporarily laminated is a center line averageroughness “Ra” (JIS B0601 (1994)) of fine irregularities on the surfacefrom 0.1 to 3.0 μm.
 20. A method for producing a protective film fortemporary lamination to a copper-mesh-layer-side surface of anelectromagnetic wave shielding sheet in which at least the copper meshlayer is provided on one surface of a transparent substrate, the methodcomprising the steps of: selecting an adhesive in which an amount offree organic acids is an amount that makes 10 or less a color differenceΔE_(L*a*b*) of the copper-mesh-layer-side surface of the electromagneticwave shielding sheet before and after the adhesive is laminated on thecopper-mesh-layer-side surface and they are left for 200 hours in anatmosphere of a temperature of 60° C. and a relative humidity of 95%,from adhesives containing a polymer having repeating units derived froman acrylic ester and/or a methacrylic ester, and therewith forming anadhesive layer on a support.